Fast acting compressible stop

ABSTRACT

A compressible stop for use in a crane has a housing, a rod slidably mounted within the housing, a floating piston, and a valve assembly. The floating piston divides the housing into a gas portion biasing the floating piston towards an end of the housing and a liquid portion containing a hydraulic fluid. The valve assembly divides the liquid portion into a support portion and a reserve portion. The valve assembly includes a check valve allowing a liquid to flow from the reserve portion into the support portion, a pressure sensitive valve inhibiting the liquid from flowing from the support portion into the reserve portion unless the pressure is above a threshold pressure, and a frangible divider configured to rupture when the liquid pressure exceeds a rupture pressure.

REFERENCE TO EARLIER FILED APPLICATIONS

The present application is a 371 National Phase application ofPCT/US16/36951 filed Jun. 10, 2016 and titled Fast Acting CompressibleStop, which in turn claims priority to and the benefit of U.S.Provisional Patent Application Ser. No. 62/174,899 filed Jun. 12, 2015and Fast Acting Compressible Stop, the disclosures of which areincorporated in their entirety by this reference.

BACKGROUND

The present invention relates to a compressible stop member for use on acrane, such as a fixed mast stop used on a mobile lifting crane, andparticularly a fast-acting compressible stop member.

Lift cranes typically include a carbody; ground engaging memberselevating the carbody off the ground; a rotating bed rotatably connectedto the carbody such that the rotating bed can swing with respect to theground engaging members; and a boom pivotally mounted on the rotatingbed, with a load hoist line extending there from. For mobile liftcranes, the ground engaging members are moveable ground engagingmembers. There are different types of moveable ground engaging members,most notably tires for truck mounted cranes, and crawlers. Typically themobile lift cranes include a counterweight to help balance the cranewhen the crane lifts a load.

A crane with a pivotable boom will typically include a mast which may befixed or live. The mast provides a lateral offset from the base of theboom for connection of a crane suspension. A fixed mast will typicallyinclude a compressible stop member, often referred to as a mast stop,used to prevent the mast from rotating backwards when there is no load,or a light load on the boom. In normal conditions, the mast stopcompresses slowly, but in the event of a sudden loss of weight on theboom, the mast stop must be able to compress quickly. Past mast stopstypically included a spring so that the mast stop can engage the mastthroughout a range of motion. The spring applies greater and greaterforce the further the mast stop is compressed. This compression providesa return force to support the mast. A conventional mast stop might bebuilt with a tube inside of a tube, with a spring inside of the tubes.If the mast stop is compressed sufficiently, the spring would becompressed until it reached a solid height, thus greatly increasing thesupport of the mast stop.

While such mast stops have proven themselves to be adequate, they have adisadvantage in that the spring and tube arrangement cannot be easilyscaled up in size due to physical limitations on the space available forthe mast stop. For example, a larger crane that has higher capacitiesmay not necessarily be proportionately larger in all dimensions. Thelarger crane will need a mast stop that can absorb more energy, but thespace in which to deploy that mast stop may not be large enough toaccommodate the larger spring and tube necessary for the mast stop.Additionally, the typical spring arrangement provides for a limitedrange of motion over which the mast stop supports the boom and thesupport that it does provide varies as the mast stop is compressed.

For larger cranes, mast stops have been developed that use hydraulics toprovide an extended range of support. Hydraulic valves may be used tocontrol the pressure of the hydraulic fluid in the mast stop. However,the flow rate of a hydraulic valve is directly related to the size ofthe valve. In order for a hydraulic compressible stop to compress at thesame rate as a conventional spring-type compressible stop, the hydrauliccompressible stop must use a large valve or multiple smaller valves.Once again, space becomes a problem, along with the added cost andcomplexity of the valves. Therefore, past mast stops using hydraulicvalves may provide an extended range of support, but typically operateslowly, due to the limitations on the valves within the hydrauliccompressible stop.

Thus there remains a need for a mast stop that can operate over a largerrange of motion, providing a consistent amount of support like ahydraulic mast stop, while being able to be compressed quickly, like aconventional mast stop.

BRIEF SUMMARY

In one aspect a stop assembly for a crane is disclosed. The stopassembly includes a housing having an internal cavity, a first housingend, and a second housing end, the second end having a passageway intothe internal cavity. A rod is slidably mounted within the housing andpasses through the passageway and a first rod end is disposed within theinternal cavity with a second rod end located external to the internalcavity. A floating piston divides the internal cavity into a gas portionbiasing the floating piston towards the second housing end and a liquidportion. A valve assembly divides the liquid portion into a supportportion and a reserve portion. The valve assembly includes a check valveallowing a liquid to flow from the reserve portion into the supportportion, a pressure sensitive valve inhibiting the liquid from flowingfrom the support portion into the reserve portion when a liquid pressureis below a threshold pressure and allowing the liquid to flow from thesupport portion to the reserve portion when the liquid is above thethreshold pressure, and a frangible divider configured to rupture whenthe liquid pressure exceeds a rupture pressure.

In some embodiments, the frangible divider is a rupture disk.

In some embodiments, the stop assembly further includes a sealable portin the housing providing access to the gas portion.

In some embodiments, one of the first housing end and the second rod endhas a crane component engagement surface and the other of the firsthousing end and the second rod end is configured for pivotal attachmentto a crane component.

In some embodiments, the stop assembly further includes a lateralsupport strut having a first end coupled to the housing and a second endconfigured to couple to a crane component.

In some embodiments, the gas portion contains a sealed volume ofcompressed gas.

In another aspect, a mobile crane is disclosed. The mobile craneincludes a carbody, ground engaging members elevating the carbody off ofthe ground, at least one support column mounted on a rotating bed, and acompressible stop. The compressible stop includes a housing having aninternal cavity, a first housing end, and a second housing end, thesecond end having a passageway into the internal cavity. A rod isslidably mounted within the housing and passes through the passagewayand a first rod end is disposed within the internal cavity with a secondrod end located external to the internal cavity. A floating pistondivides the internal cavity into a gas portion biasing the floatingpiston towards the second housing end and a liquid portion. A valveassembly divides the liquid portion into a support portion and a reserveportion. The valve assembly includes a check valve allowing a liquid toflow from the reserve portion into the support portion, a pressuresensitive valve inhibiting the liquid from flowing from the supportportion into the reserve portion when a liquid pressure is below athreshold pressure and allowing the liquid to flow from the supportportion to the reserve portion when the liquid is above the thresholdpressure, and a frangible divider configured to rupture when the liquidpressure exceeds a rupture pressure.

In some embodiments, at least one of the first crane component and thesecond crane component is selected from the group consisting of a mast,a boom, a gantry, and a rotating bed. In some embodiments, both thefirst crane component and the second crane component are supportcolumns. In some embodiments, one of the first interface and the secondinterface is a rotating connection and the other of the first interfaceand the second interface comprises a U-shaped engagement surface.

In some embodiments, the frangible divider is a rupture disk.

In some embodiments, there is a sealable port in the housing providingaccess to the gas portion. In some embodiments, the gas portion is asealed volume of compressed gas.

In some embodiments, the mobile crane further includes a lateral supportstrut having a first end coupled to the housing and a second end to thefirst crane component.

In another aspect, a method of allowing a support column pivotallymounted to a crane component to rotate beyond a normal stop position inresponse to a sudden load change is disclosed. The method includesproviding a compressible stop including a housing, a rod, and a floatingpiston. The housing has an internal cavity, a first housing end, and asecond housing end, the second end has a passageway into the internalcavity. The rod is slidably mounted within the housing and passesthrough the passageway and a first rod end is disposed within theinternal cavity with a second rod end located external to the internalcavity. The floating piston divides the internal cavity into a gasportion biasing the floating piston towards the second housing end and aliquid portion. A valve assembly divides the liquid portion into asupport portion and a reserve portion. The valve assembly includes acheck valve allowing a liquid to flow from the reserve portion into thesupport portion, a pressure sensitive valve inhibiting the liquid fromflowing from the support portion into the reserve portion when a liquidpressure is below a threshold pressure and allowing the liquid to flowfrom the support portion to the reserve portion when the liquid is abovethe threshold pressure, and a frangible divider configured to rupturewhen the liquid pressure exceeds a rupture pressure.

One of the first interface and the second interface is attached to oneof the support column and the crane component. The support column isrotated towards the crane component until the other of the firstinterface and the second interface contacts the other of the supportcolumn and the crane component. The support column is rotated towardsthe crane component with the other of the first interface and the secondinterface in contact with the other of the support column and the cranecomponent thereby compressing the compressible stop causing the pressureof the liquid in the support portion to reach the threshold pressure andto flow through the pressure sensitive valve into the reserve portion.The support column is towards the crane component with the other of thefirst interface and the second interface in contact with the other ofthe support column and the crane component, thereby compressing thecompressible stop causing the pressure of the liquid in the supportportion to exceed the rupture pressure rupturing the frangible divider.

In some embodiments, the method further includes inhibiting rotation ofthe support column towards the crane component with the compressiblestop when the liquid pressure in the support section is below thethreshold pressure.

In some embodiments, the method further includes rotating the supportcolumn away from the crane component, extending the first interface tomaintain contact with the other of the support column and the cranecomponent, and forcing the liquid through the check valve from thereservoir portion into the support portion. In some embodiments, theliquid is forced through the check valve by a pressurized gas in the gassection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a mobile crane.

FIG. 2 illustrates an enlarged view of the rotating bed of the mobilecrane of FIG. 1.

FIG. 3 illustrates another mobile crane having a compressible stopmember.

FIG. 4 illustrates an exemplary embodiment of a fast acting compressiblestop.

FIG. 5 illustrates a schematic sectional view of the second end of thecompressible stop of FIG. 4.

FIG. 6 illustrates an exemplary pressure sensitive valve assembly.

FIG. 7 illustrates an exemplary pressure sensitive valve.

FIG. 8 illustrates an exemplary rupture disk.

DETAILED DESCRIPTION

The present invention will now be further described. In the followingpassages, different aspects of the invention are defined in more detail.Each aspect so defined may be combined with any other aspect or aspectsunless clearly indicated to the contrary. In particular, any featureindicated as being preferred or advantageous may be combined with anyother feature or features indicated as being preferred or advantageous.

While the described embodiments will have applicability to many types ofcranes, it will be described in connection with mobile lift crane 10,shown in an operational configuration in FIG. 1 and in an enlarged viewin FIG. 2. The mobile lift crane 10 generally includes lower works andupper works. The lower works include a carbody 12 and moveable groundengaging members in the form of crawlers 14. The upper works include arotating bed 24, support columns in the form of a boom 16 and a mast 18,boom suspension 20, and a counter weight assembly 22. There are twocrawlers 14, one on either side of the crane 10, only one of which canbe seen from the side views of FIG. 1 and FIG. 2. In the crane 10, theground engaging members could be multiple sets of crawlers, one set ofcrawlers on each side. Of course additional crawlers than those showncan be used, as well-as other types of ground engaging members, such astires.

The rotating bed 24 is mounted to the carbody 12 with a slewing ring 26,such that the rotating bed 24 can swing about an axis with respect tothe ground engaging members 14. The rotating bed 24 supports the boom 16pivotally mounted on a front portion of the rotating bed 24; the mast 18mounted at its first end on the rotating bed 24; and the counterweightunit 22 unit is mounted to the rear of the rotating bed. Thecounterweight unit 22 may be in the form of multiple stacks ofindividual counterweight members on a support member.

The boom suspension 20 between the top of mast 18 and the boom 16 isused to control the boom angle and transfer load so that thecounterweight unit 22 can be used to balance a load lifted by the crane10. A load hoist line (not shown) is trained over a pulley (usuallymultiple sheaves in a sheave set) on the boom 16, supporting a hook 28.At the other end, the load hoist line is wound on a first main loadhoist drum (not shown) connected to the rotating bed 24. The rotatingbed 24 includes other elements commonly found on a mobile lift crane,such as an operator's cab 30, hoist drum for the boom hoist rigging 20,a second main hoist drum and an auxiliary load hoist.

The boom suspension 20 includes a boom hoist line in the form of wirerope wound on a boom hoist drum (not shown), and reeved through sheavesof an equalizer 47. The boom suspension 20 includes fixed lengthpendants connected between the boom top and an upper portion of theequalizer 47. The lower portion of the equalizer 47 is connected to therotating bed 24 though the mast 18. This arrangement allows rotation ofthe boom hoist drum to change the amount of boom hoist line between thelower portion of the equalizer 47 and the upper portion of the equalizer47, thereby changing the angle between the rotating bed 24 and the mast18, which causes the boom 16 to move through the fixed length pendants.

The mobile crane 10 includes a boom stop 32 and a mast stop 34. The boomstop 32 and mast stop 34 prevent the respective crane components fromrotating into a particular configuration and provide additional support.For example, boom stop 32 may prevent the boom 16 from rotating into avertical position. Mast stop 34 may prevent the mast 18 from rotatingtowards the counterweight 22 when a load on the hook 28 is reduced.While mast 18 is fixed, during setup and operation, some degree ofmovement of the mast 18 is necessary for proper operation.

While the boom stop 32 and the mast stop 34 are each shown as a singlemember, preferably the crane 10 includes stop members in sets of two.However, each of the stop members in the set of two is nearly identical,and placed on the crane 10 such that only one of them can be seen fromthe side views of FIGS. 1 and 2. Further description of the stop memberswill be done in reference to a single mast stop 34, but it will beunderstood that multiple stop members may be used and the description isapplicable to other stop members on the crane 10, both those explicitlycalled out in FIGS. 1 and 2, as well as other stop members which may notbe explicitly illustrated in FIGS. 1 and 2.

FIG. 3 illustrates another embodiment of a mobile crane 50 showing analternative mast stop 34 placement. The mobile lift crane 50 includes acarbody 12, crawlers 14, a boom 16, a mast 18, boom suspension (notshown), and a counter weight assembly 22. A rotating bed 24 is mountedto the carbody 12 with a slewing ring 26, such that the rotating bed 24can swing about an axis with respect to the ground engaging members 14.The mobile crane 50 includes a boom stop 32 and a mast stop 34. The maststop of FIG. 3 differs from the mast stop of FIG. 1 in that it does notinterface with the rotating bed 24, and instead interfaces with a backhitch 33 of the mobile crane 50.

FIG. 4 illustrates an exemplary embodiment of a compressible stop 100.FIG. 5 illustrates a sectional schematic of a portion of thecompressible stop 100 of FIG. 4. The compressible stop 100 will bedescribed in relation to FIG. 4 and FIG. 5. Compressible stop 100 is amast stop 34, but may be used in other applications such as a boom stopor jib stop. Additionally, features of the described embodiment may beused in other stop members such as a boom stop, jib stop, or other stopmembers on a crane. The compressible stop 100 has an elongated housing102 with an internal cavity 104 (visible in FIG. 5). A first end 106 ofthe elongated housing 102 is configured to interact with a first cranecomponent and a second end 108 has a passageway 107 into the internalcavity 104. In the embodiment of FIG. 4, the housing 102 is cylindricaland the cavity 104 is cylindrical as well.

A rod 112 is slidably mounted within the housing 102 and passes throughthe passageway 107 at the second end 108 of the housing 102. A first end113 of the rod 112 is disposed within the internal cavity 104 and asecond end 114 of the rod 112 opposite the first end 113 is locatedexternal to the internal cavity 104. The first end 106 of the housing102 and the second end 114 of the rod 112 each have an interface forinteracting with a crane component. There are generally two differentstyles of interfaces that are used and a stop member typically includesone of each style. Other styles of interfaces are possible and these aremerely two examples.

The first style of interface is exemplified by the first end 106 of thehousing 102. The first style of interface includes a U-shaped member 110having a support surface for interacting with a first crane component.The U-shaped member 110 is sized and shaped to receive a correspondinginterface of a first crane component. For example, the first cranecomponent could be the rotating bed 24 and the interface could be ahorizontal cylinder offset from the crane component. When the first end106 of the housing 102 is moved towards the first component, theinterface will eventually contact the first crane component and preventfurther movement of the interface relative to the crane component.

The second style of interface is exemplified by the second end 114 ofthe rod 112. The second end 114 of the rod 112 includes extensions 116,each of which has a hole for receiving a pin. The second interface maybe coupled to a second crane component, such as a mast 16, by aligningthe holes of the extensions 116 over a complementary hole on the secondcrane component and inserting a pin through the extensions 116. Thepinned connection results in a pivoting connection in which theinterface is pivotable about an axis of the pin.

The embodiment of FIG. 4 is shown with the first interface type on thefirst end 106 of the housing 102 and the second interface type on thesecond end 114 of the rod 112. However, in some embodiments the firstend 106 of the housing 102 may have the second interface type and thesecond end 114 of the rod 112 may have the first interface type. Forexample, the first end 106 of the housing 102 could have a pinnedconnection for connection to a crane component such as a mast 16, andthe second end 114 of the rod 112 could have a U-shaped member forengaging a rotating bed 24.

The housing 102 has an optional lateral support strut 118 for connectionto a crane component for additional lateral stability. If one of theinterfaces of the compressible stop 100 is rigid, or if the compressiblestop 100 is support by some other means, the lateral support strut 118is not necessary. A first end 120 of the lateral support strut 118 iscoupled to the housing 102 and a second end 122 of the lateral supportstrut 118 is configured to couple to a crane component. For example, thefirst and second end 120, 122 may each have at least one extension witha pin hole for receiving a pin. The pin holes may be aligned withcorresponding pin holes on crane components and pins inserted to securethe lateral support strut 118. In some embodiments, the lateral supportstrut 118 may itself be a compressible stop member.

As shown in FIG. 5, the housing 102 has a floating piston 124 thatseparates the internal cavity 104 into a gas portion 126 and a liquidportion 128. The floating piston 124 forms a fluid seal between the gasportion 126 and the liquid portion 128, so that fluid in the twoportions 126, 128 does not flow past the floating piston 124 into theother portion 126, 128. A gas in the gas portion 126 is pressurized tobias the floating piston 124 towards the second end 108 of the housing102. The bias may be increased or decreased by adjusting the gaspressure in the gas portion 126. A port 130 in a wall of the housing 102provides access to the gas portion 126, allowing gas to be introduced orremoved to adjust the pressure as necessary. Once the gas is at thedesired pressure, the port 130 is closed, sealing the gas portion. Inone embodiment, the gas portion 126 is precharged to two hundred poundsper square inch of pressure. The pressure of the gas in the gas portion126 will vary in use, as the floating piston 124 changes the volume ofthe gas portion 126. In some embodiments, a conventional spring may beused in place of the compressed gas to provide the bias of the floatingpiston 124. The spring may be preloaded to provide a greater bias to thefloating piston 124.

The liquid portion 128 contains a liquid such as hydraulic fluid. Avalve assembly 132 divides the liquid portion 128 into a reservoirsection, or reserve portion, 134 and a support section 136. The valveassembly 132, shown in detail in FIG. 6, contains a check valve and apressure sensitive valve. The check valve prevents liquid flowing fromthe support section to the reservoir section, while allowing liquid toflow in the opposite direction. The pressure sensitive valve remainsclosed until a threshold pressure is reached, at which point it allowsliquid to flow in either direction. In the embodiment of FIG. 6, thecheck valve and the pressure sensitive valve are combined into onesequence valve 133.

FIG. 7 illustrates the sequencing valve 133 removed from the valveassembly 132. The sequencing valve 133 has an inlet 135 in fluidcommunication with the support section 136, an outlet 137 in fluidcommunication with the reservoir section 134, and a drain 139 in fluidcommunication with the reservoir section 134. The sequencing valve 133has a built-in check valve, allowing liquid to flow from the outlet 137to the inlet 135, but preventing liquid flowing from the inlet 135 tothe outlet 137 until a threshold pressure differential between the inlet135 and the drain 139 is reached. When the pressure differential betweenthe drain 139 and the inlet 135 exceeds the threshold pressure, thesequencing valve 133 opens allowing liquid to flow from the inlet 135 tothe outlet 137. If the pressure differential drops below the thresholdpressure, the sequencing valve 133 closes, preventing further liquidflow from the inlet 135 to the outlet 137. The threshold pressure may beadjusted by turning an adjustment screw 150. In some embodiments, thethreshold pressure is set at two-thousand three hundred pounds persquare inch. Because the pressure in the reservoir section 134 is muchlower than the pressure in the support section 136, the pressuredifferential is approximated using just the pressure in the supportsection 136. However, if greater accuracy is required, or if thepressure in the reservoir section 134 is not negligible, it may be usedwhen calculating the threshold pressure.

Returning to FIG. 6, the sequencing valve 133 is placed in the valveassembly 132 perpendicular to the housing 102. The adjustment screw 150is visible in FIG. 6, showing the orientation of the sequencing valve133. The liquid may pass through the valve assembly 132 only through thesequence valve 133. In some embodiments, the function of the check valveand pressure sensitive valve may be performed by separate components,rather than a single sequencing valve 133 shown in FIG. 6. The outlet137 of the sequencing valve 133 opens at port 140 in the valve assembly132 and the drain 139 opens at port 142. The first end 113 of the rod112 forms a liquid seal with the internal cavity 104 so that the liquidportion 128 is sealed within the internal cavity 104. The valve assembly132 further contains a frangible divider between the reservoir section134 and the support section 136 that ruptures when the pressure in thesupport portion 136 exceeds a rupture pressure.

Operation of the compressible stop 100 will be described in relation toFIGS. 4, 5, and 6. The compressible stop 100 generally has fouroperating configurations. The first configuration occurs when thecompressible stop 100 is supporting a first component such as a mast 18relative to a second component, the second configuration occurs when thefirst component is moving towards a second component, compressing thecompressible stop 100, the third configuration occurs when the firstcomponent is moving away from the second component relieving the load onthe compressible stop 100, and the fourth configuration occurs when thefirst component moves rapidly towards the second component causing theliquid to attempt to flow through the valve assembly 132 at a rategreater than a flow rate of the sequencing valve 133.

In the first configuration, the first end 106 of the housing 102, or thesecond end 114 of the rod 112 if the compressible stop 100 is reversed,is in contact with the second component and the second end 114 of therod 112, or the first end 106 of the housing 102, is in contact with thefirst component. The compressible stop 102 supports the first componentas long as the pressure in the support portion 136 does not exceed thethreshold pressure of the pressure sensitive valve. Because the pressuresensitive valve only opens when the threshold pressure is exceeded,below the threshold pressure the support portion 136 is essentiallyincompressible and the compressible stop 100 acts as if it had a fixedlength. For example, if the first end 114 of the rod 112 had crosssectional area of fifty square inches and the threshold pressure wastwo-thousand three hundred pounds per square inch, the compressible stop100 would act as if it had a fixed length up to a compressive force ofone hundred fifteen thousand pounds. In some embodiments, the pressuresensitive valve may have an adjustable threshold pressure, such that thecompressive force required to compress the compressible stop 100 may beadjustable.

Once the compressive load on the compressible stop 100 causes thepressure in the support portion 136 to exceed the threshold pressure,the pressure sensitive valve begins to allow liquid to flow through thevalve assembly 132 into the reservoir portion 134. This allows thesupport portion 136 to decrease in volume and the first end 113 of therod 112 moves towards the valve assembly 132, decreasing the length ofthe compressible stop 100. The pressure within the support portion 136remains at the threshold pressure so that the compressible stop 100still provides a support to the first crane component. The liquidflowing through the pressure sensitive valve increases the amount ofliquid in the reservoir portion 134. Because the liquid isincompressible, the only way for an increased amount of liquid to flowinto the reservoir portion 134 is for the reservoir portion 134 toexpand in volume. It does so by forcing the floating piston 124 towardsthe first end 106 of the housing 102, compressing the gas contained inthe gas portion 126. The compressible stop 100 will continue to compressin length until the compressive force is reduced below the thresholdamount or until the support portion 136 is essentially empty of liquidand the first end 113 of the rod 112 contacts the valve assembly 132 orsome other hard stop.

In the third configuration, the crane component is moving away from thecompressible stop 100, removing the load from the rod 112. Thecompressible stop 100 expands lengthwise to maintain contact between thefirst and second crane components up to the maximum extended length ofthe compressible stop 100. The check valve of the valve assembly 132allows the liquid in the reservoir portion 134 to flow back into thesupport section 136 as the first end 113 of the rod 112 moves away fromthe valve assembly 132. The pressurized gas pressurizes the liquid inthe reservoir portion 134 and the liquid flows through the check valveuntil the pressure in the support portion 136 equals the pressure in thereservoir portion 134. If the pressure is great enough, it will causethe rod 112 to extend from the housing 102, or the rod 112 may be pulledout of the housing 102 due to interactions with other crane componentsor gravity.

As the rod 112 extends, the compressible stop 100 maintains closecontact with each of the crane components. When the first cranecomponent is moved back towards the second crane component compressingthe compressible stop 100 again, the check valve closes and the liquidin the support portion 136 once again inhibits the compression of thecompressible stop 100, supporting the crane component in its newposition.

In rare instances, the first component may be required to move rapidlytowards the second crane component. For example, if a load is suddenlyremoved from the hook 28 on the boom 16, the mast 18 may be pulledtowards the counterweight. This rapid movement may exceed the flow rateof the pressure sensitive valve; causing a buildup of pressure in thesupport portion 136. The pressure builds up until it reaches the rupturepressure as determined by the frangible divider. In some embodiments,the rupture pressure is six thousand pounds per square inch. Once therupture pressure is reached, the frangible divider breaks, opening anadditional passage between the support portion 136 and the reservoirportion 134. The additional passage allows the liquid to rapidly passthrough the valve assembly 132 and the compressible stop 100 is able tocompress rapidly, beyond the rate allowed by the pressure sensitivevalve. In some embodiments the flow rate of the pressure sensitive valveis sixty gallons per minute and the flow rate of the rupture disk afterrupture is five hundred gallons per minute.

FIG. 6 illustrates an embodiment of a valve assembly 132 having a checkvalve 142, a pressure sensitive valve 140, and a frangible divider inthe form of a rupture disk 138 (shown removed). FIG. 8 illustrates across section of the rupture disk 138. When the pressure differentialbetween a first side 152 of the rupture disk 138 and a second side 154of the rupture disk 138 is exceeded, the rupture disk 138 fails,allowing liquid to flow from the first side 152 to the second side 154.

Referring to FIGS. 6 and 8, the valve assembly 132 has a through hole144 sized to receive the rupture disk 138. The through hole 144 has aportion with an internal thread, and the rupture disk 138 has anexternal thread 156 complementary to the internal thread of the throughhole 144. The rupture disk 138 is installed by threading it into thethrough hole 144 for normal operation of the valve assembly 132. Thevalve assembly 132 is coupled to the housing 102 through threadedfasteners 146. The housing 102 may be dismantled by removing thethreaded fasteners 146 to access the valve assembly 132. In the eventthe rupture disk 138 has ruptured, it may be replaced by threading a newrupture disk 138 in its place.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein may be made. Forexample, the first and second crane members need not be a boom and ajib. For example, the first crane member could be the rotating bed ofthe crane. Additionally, in some embodiments the angle at which thegravity actuated mechanism changes configurations may be other thanhorizontal. Such changes and modifications can be made without departingfrom the spirit and scope of the present invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

The invention claimed is:
 1. A stop assembly for a crane, the stopassembly comprising: a housing having an internal cavity, a firsthousing end, and a second housing end, the second end having apassageway into the internal cavity; a rod slidably mounted within thehousing and passing through the passageway, a first rod end disposedwithin the internal cavity, and a second rod end located external to theinternal cavity; a floating piston dividing the internal cavity into agas portion biasing the floating piston towards the second housing end,and a liquid portion; a valve assembly dividing the liquid portion intoa support portion and a reserve portion, the valve assembly comprising acheck valve allowing a liquid to flow from the reserve portion into thesupport portion, a pressure sensitive valve inhibiting the liquid fromflowing from the support portion into the reserve portion when a liquidpressure is below a threshold pressure and allowing the liquid to flowfrom the support portion to the reserve portion when the liquid pressureis above the threshold pressure, and a frangible divider configured torupture when the liquid pressure exceeds a rupture pressure.
 2. The stopassembly of claim 1, wherein the frangible divider comprises a rupturedisk.
 3. The stop assembly of claim 1, further comprising a sealableport in the housing providing access to the gas portion.
 4. The stopassembly of claim 1, wherein one of the first housing end and the secondrod end comprises a crane component engagement surface and the other ofthe first housing end and the second rod end is configured for pivotalattachment to a crane component.
 5. The stop assembly of claim 1,further comprising a lateral support strut having a first end coupled tothe housing and a second end configured to couple to a crane component.6. The stop assembly of claim 1, wherein the gas portion comprises asealed volume of compressed gas.
 7. The stop assembly of claim 1,wherein the valve assembly is coupled to the housing.
 8. A mobile cranecomprising: a carbody; ground engaging members elevating the carbody offof the ground; at least one support column mounted on a rotating bed; acompressible stop comprising: a housing having an internal cavity, afirst housing end having a first interface interfacing with a firstcrane component, and a second housing end having a passageway into theinternal cavity; a rod slidably mounted within the housing and passingthrough the passageway, a first rod end disposed within the internalcavity, and a second rod end located external to the internal cavity andhaving a second interface for interfacing with a second crane component;a floating piston dividing the internal cavity into a gas portionbiasing the floating piston towards the second housing end, and a liquidportion; a valve assembly dividing the liquid portion into a supportportion and a reserve portion, the valve assembly comprising a checkvalve allowing a liquid to flow from the reserve portion into thesupport portion, a pressure sensitive valve inhibiting the liquid fromflowing from the support portion into the reserve portion when a liquidpressure is below a threshold pressure and allowing the liquid to flowfrom the support portion to the reserve portion when the liquid pressureis above the threshold pressure, and a frangible divider configured torupture when the liquid pressure exceeds a rupture pressure.
 9. Themobile crane of claim 8, wherein at least one of the first cranecomponent and the second crane component is selected from the groupconsisting of a mast, a boom, a gantry, and the rotating bed.
 10. Themobile crane of claim 8, wherein both the first crane component and thesecond crane component comprise a support column.
 11. The mobile craneof claim 8, wherein one of the first interface and the second interfacecomprises a rotating connection and the other of the first interface andthe second interface comprises a U-shaped engagement surface.
 12. Themobile crane of claim 8, wherein the frangible divider comprises arupture disk.
 13. The mobile crane of claim 8, further comprising asealable port in the housing providing access to the gas portion. 14.The mobile crane of claim 8, further comprising a lateral support struthaving a first end coupled to the housing and a second end to the firstcrane component.
 15. The mobile crane of claim 8, wherein the gasportion comprises a sealed volume of compressed gas.
 16. A method ofallowing a support column pivotally mounted to a crane component torotate beyond a normal stop position in response to a sudden loadchange, the method comprising: providing a compressible stop comprising:a housing having an internal cavity, a first housing end having a firstinterface interfacing with a first crane component, and a second housingend having a passageway into the internal cavity; a rod slidably mountedwithin the housing and passing through the passageway, a first rod enddisposed within the internal cavity, and a second rod end locatedexternal to the internal cavity and having a second interface forinterfacing with a second crane component; a floating piston dividingthe internal cavity into a gas portion biasing the floating pistontowards the second housing end, and a liquid portion; a valve assemblydividing the liquid portion into a support portion and a reserveportion, the valve assembly comprising a check valve allowing a liquidto flow from the reserve portion into the support portion, a pressuresensitive valve inhibiting the liquid from flowing from the supportportion into the reserve portion when a liquid pressure is below athreshold pressure and allowing the liquid to flow from the supportportion to the reserve portion when the liquid pressure is above thethreshold pressure, and a frangible divider configured to rupture whenthe liquid exceeds a rupture pressure; attaching one of the firstinterface and the second interface to one of the support column and thecrane component; rotating the support column towards the crane componentuntil the other of the first interface and the second interface contactsthe other of the support column and the crane component; rotating thesupport column towards the crane component with the other of the firstinterface and the second interface in contact with the other of thesupport column and the crane component thereby compressing thecompressible stop causing the pressure of the liquid in the supportportion to reach the threshold pressure and to flow through the pressuresensitive valve into the reserve portion; and rotating the supportcolumn towards the crane component with the other of the first interfaceand the second interface in contact with the other of the support columnand the crane component thereby compressing the compressible stopcausing the pressure of the liquid in the support portion to exceed therupture pressure rupturing the frangible divider.
 17. The method ofclaim 16, further comprising inhibiting rotation of the support columntowards the crane component with the compressible stop when the liquidpressure in the support portion is below the threshold pressure.
 18. Themethod of claim 16, further comprising: rotating the support column awayfrom the crane component; extending the first interface to maintaincontact with the other of the support column and the crane component;and forcing the liquid through the check valve from the reservoirportion into the support portion.
 19. The method of claim 18, whereinthe liquid is forced through the check valve by a pressurized gas in thegas portion.